The Collaborative International Dictionary of English v.0.48:

Whack \Whack\, v. t. [imp. & p. p. Whacked; p. pr. & vb. n.
   Whacking.] [Cf. Thwack.]
   1. To strike; to beat; to give a heavy or resounding blow to;
      to thrash; to make with whacks. [Colloq.]
      [1913 Webster]

            Rodsmen were whackingtheir way through willow
            brakes.                               --G. W. Cable.
      [1913 Webster]

   2. To divide into shares; as, to whack the spoils of a
      robbery; -- often with up. [Slang]
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

whacked
    adj 1: (British informal) exhausted or worn out

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "whacked":
   all in, beat, beat up, beaten, bone-weary, bushed, dead,
   dead-and-alive, dead-tired, deadbeat, dog-tired, dog-weary, done,
   done in, done up, drained, exhausted, fagged out, gone,
   knocked out, played out, pooped, pooped out, prostrate,
   ready to drop, spent, tired out, tired to death, tuckered out,
   used up, washed-up, weary unto death, wiped out, worn-out